Communication and Homeostasis (5) Flashcards
1
Q
What is the purpose of homeostasis?
A
- animals increase their chances of survival by responding to external stimuli like changes in their external environment
- they also respond to internal changes to maintain optimum conditons for thier metabolism
2
Q
What is a stimulus?
A
- Any change in the internal or external environment is called a stimulus
3
Q
What are receptors and how do they work?
A
- a receptor detects stimuli, they are extremely specific and tend to detect a particular stimulus.
- some receptors are cells while some are proteins on cell surface membranes
4
Q
What are effectors?
A
Effectors are cells that bring about a response to a stimulus, to produce an effect. Effectors can be glands or muscles.
5
Q
What happens for the body to produce a response?
A
To produce a response, receptors need to communicate with effectors which in turn may need to communicate with other cells. This happens via cell signalling.
6
Q
How is cell signaling used in producing a response?
A
Cell signaling can occur between adjacent or distant cells.
- nervous system cells use chemicals calle neurotransmitters in the form of cell signalling between adjacent neurones
- hormone system uses secreted hormones which travel in the blood to distant cells
7
Q
What is homeostasis?
A
Homeostasis involves control systems that keep your internal environment roughly constant. This is important as it is vital for cells to function normally and to stop them from being damaged.
8
Q
What is the optimum internal temperature in humans?
A
37 degrees
8
Q
Why is thermoregulation particularly important?
A
It is important to maintain the right core body temperature. This is because temperature affects enzyme activity, and enzymes control the rate of metaboic reactions.
8
Q
What is the process of negative feedback?
A
Receptors detect when a level is too high or too low and the information is communicated through the nervous or hormonal system to effectors which bring the level back to normal
8
Q
When can negative feedback sometimes not work?
A
When the change is too extreme sometimes the negative feedback process cannot sucessfully bring it back to nromal levles. e.g a sudden drop in internal temperature to hypothermic levels cannot be easily brought back to normal
9
Q
What is positive feedback and how does it work?
A
Positive feedback mechanisms are when the body amplifies the change to further increase the level from the normal level.
e.g increase platelets in blood when injured.
Positive feedback is useful to rapidly activate somethng
9
Q
Why is positive feedback not used in homeostasis?
A
It doesn’t keep your internal environment constant.
9
Q
What is the nervous system?
A
It is a complex network of cells called neurones that work in electrical communication throughout the body to transfer information
9
Q
What do sensory neurons do?
A
Sensory neurones transmit nerve impulses from receptors to the central nervous system
9
Q
What do motor neurones do?
A
Motor neurones transmit nerve impulses from the CNS to the effectors
9
Q
What do relay neurones do?
A
Relay neurones transmit nerve impulses between sensory neurones and motor neurones
9
Q
What is the passage a nerve impuse makes throughout the nervous system?
A
- stimulus
- receptors detect the stimulus
- the sensory neurone transmits an electrical impulse to the CNS
- the CNS with the relay neurone decides what to do with the information recieved
- the motor neurone transmits an electrical impulse to the effector
- the effector brings about a response
- response
10
Q
Why do we need different receptors for different forms of stimuli?
A
Different stimuli have different forms of energy. However your nervous system only sends information in the form of nerve impulses.
11
Q
What do sensory receptors do and why are they considered transducers?
A
Sensory receptors convert the energy of a stimulus into electrical energy. So, sensory receptors act as transducers.
12
Q
What is a transducer?
A
Something that converts one form of energy into another
13
Q
What is a nervous system receptor like in it resting state?
A
In its resting state it is not being stimulated, there is a difference in charge between the inside and outside of the cell. This difference creates a voltage which is called a potential difference.
14
Q
What is resting potential-generator potential conversion process?
A
When a stimulus is detected, the cell membrane is excited and becomes more permeable, allowing more ions to move in and out of the cell which alters the potential difference. This change in potential difference is called the generator potential
15
Q
What causes a bigger generator potential to be formed?
A
A bigger stimulus excited the membrane more, causing a bigger movement of ions and a bigger change in potential difference, so a bigger generator potential is formed?
16
How do generator potentials lead to an action potential?
If the generator potential is big enough it'll trigger an action potential along a neurone. An action potential is only triggered if the generator potential reaches a certain level called the threshold level.
17
What happens when a stimulus is too weak?
If the stimulus is too weak the generator potential wont reach the threshold, so there's no action potential.
18
What is the general structure of neurones?
All neurons have:
- cell body
- dendrites/dendrons towards the cell body
- axons away from the cell body
19
What is the structure and function of a sensory neurone?
Sensory neurons have short dendrites and one long dendron to carry nerve impulses from receptor cells to the cell body, and one short axon that carries impulses from the cell body to the CNS
20
What is the structure and function of a relay neurone?
Motor neurones have many short dendrites that carry nerve impulses from the central nervous system to the cell body, and one long axon that carries nerve impulses from the cell body to effector cells.
21
What is the structure and function of a motor neurone?
Relay neurones have many short dendrites that carry nerve impulses from sensory neurones to the cell body, and one axon that carries nerve impulses from the cell body to motor neurones
22
Which neurones are myelinated?
Only relay neurones are not myelinated as they are so short it wouldn't make much difference in the speed of the electrical impulse.
23
What is a neurones resting state?
This is the state of a neurone when it isn't being stimulated. The outside of the membrane is positively charged compared to the inside. This is because there are more positive ions outside of the cell than inside. (polarised membrane)
24
What is the value for a neurones resting state?
around -70 mv
25
How is a neurones' resting potential and state maintained?
It is regulated by sodium-potassium pumps and potassium ion channels in a neurones membrane.
26
How do do sodium-potassium pumps maintain resting potential?
The pumps move 3 sodium ions out of the cell for each 2 potassium ions entering. As the sodium ions cannot diffuse back in this creates an electrochemical gradient as the inside of the cell membrane is more negative than the outside. The membrane also becomes even more negative as potassium ions diffuse out of the membrane via potassium ion channels as the membrane is permeable to these ions.
27
What are the steps in a neurone to develop an action potential in response to a stimulus?
1. The stimulus causes the sodium ion channels to open so the membrane is more permeable to sodium ions and there is an influx into the cell. This makes the inside membrane less negative
2. If it reaches the threshold level, the voltage gated ion channels open and even more sodium ions move in as a form of positive feedback. (Depolarisation)
3. When a potential difference of around 30 mv is reached the sodium ion channels close and the potassium channels open so potassium ions diffuse out of the neurone as an attempt to get the membrane back to its negative resting state. (Repolarisation)
4. As the potassium ion channels are slow to close there is a slight overshoot so too many potassium ions have left and the membrane is too negative. (hyperpolarisation)
5. The sodium-potassium pump helps return the membrane back to its original resting potential until it's excited by another stimulus.
28
Why can the neurone not be excited again directly after an action potential?
The ion channels are recovering and they can't be made to open. This period of recovery is called the refractory period.
28
What is the same across all action potentials?
An action potential will always fire with the same change in voltage, no matter how big the stimulus is.
29
What actually is an action potential?
When an action potential happens some of the sodium ions diffuse sideways which causes sodium channels in the next region to open and sodium ions to diffuse into that area. This causes a wave of depolarisation to travel along the neurone. The wave more away from the aprts of the membrane in the refractory period because these parts can't fire an action potential.
30
What happens to an action potential if the threshold is not reached?
If the threshold isn't reached, an action potential won't fire. This is the all-or-nothing nature of action potentials.
31
How will a bigger stimulus affect the neurone?
A bigger stimulus won't cause a bigger action potential, but it will cause them to fire more frequently- and the brain identifies this and will response accordingly.
32
What is the purpose of the myelin sheath in neurones?
The schwann cells are made of lipids which act as an electrical insulator. Between the cells are small patches of bare membrane called nodes of ranvier where there is a high concentration of sodium ion channels.
33
How do myelinated neurones work with saltatory conduction?
The neurones cytoplasm conducts enough electrical charge to depolarise the next node so the impulse jumps from node to node which makes transmission really fast.
34
What is a synapse?
A synapse is the junction between a neurone and another neurone or between a neurone and an effector cell.
35
What is the synaptic cleft?
The tiny gap between the cells at a synapse is called the synaptic cleft
36
What is the presynaptic neurone?
This is the neurone before the synapse and it has a swelling called a synaptic knob. This contains synaptic vesicles filled with chemicals called neurotransmitters.
37
What happens when an action potential reaches the end of a neurone at the synaptic cleft?
They trigger neurotransmitters to be released into the synaptic cleft. They diffuse across to the postsynaptic membrane and bind to specific receptors.
38
What happens when neurotransmitters bind to receptors on the postsynaptic membrane?
They might trigger another action potential
They might cause a muscle contraction
They might cause a hormone to be secreted
39
Why are neurotransmitters removed from the synaptic cleft after use?
They are broken down by enzymes to make sure that the response doesn't accidentally happen again
40
What are some examples of neurotransmittes?
Acetylcholine and noradrenaline
41
What synapses use Acetylcholine?
Cholinergic synapses. They bind to receptors called cholinergic receptors, and they're broken down by an enzyme called acetylcholinesterase
42
How do neurotransmitters transmit nerve impulses between neurones?
1. An action potential triggers a calcium influx
2. The calcium influx triggers the release of a neurotransmitter
3. The neurotransmitter triggers an action potential in the postsynaptic neurone
43
How does an action potential trigger a calcium influx in the synaptic knob?
- an action potential arrives as the synaptic knob of the presynaptic neurone
- the action potential stimulates voltage gated calcium ion channels in the presynaptic neurone to open
- Calcium ions diffuse into the synaptic knob
44
How does a calcium influx cause the release of a neurotransmitter?
- The influx of calcium ions into the synaptic knob causes the synaptic vesicles to move to the presynaptic membrane. They then fuse with the presynaptic membrane
- The vesicles release the neurotransmitter into the synaptic cleft by exocytosis
45
How does a neurotransmitter trigger an action potential in the postsynaptic neurone?
- The neurotransmitter diffuses across the synaptic cleft and binds to specific receptors on the postsynaptic membrane
- This causes sodium ion channels in the postsynaptic neurone to open. The influx of sodium ions into the postsynaptic membrane causes depolarization. An action potential on the postsynaptic membrane is generated if the threshold is reached.
- The neurotransmitter is removed from the synaptic cleft so the response doesn't keep happening
46
What happens at an excitatory synapse?
Neurotransmitters depolarise the postsynaptic membrane, making it fire an action potential if the threshold is reached.
47
What happens at an inhibitory synapse?
When neurotransmitters bind to receptors on the postsynaptic membrane, they hyperpolarise the membrane which prevents an action potential from being fired.
48
What is synaptic divergence?
When one neurone connects to many neurones information can be dispersed to different parts of the body.
49
What is synaptic convergence?
When many neurones connect to one neurone information can be amplified.
50
What is spacial summation?
- When neurones converge the small amount of neurotransmitter released from each neurone can be enough altrogehter to reach the threshold in the postsynaptic neurone and trigger an action potential
- If some neurones release an inhibitory neurotransmitter then the total effect of all the neurotransmitters might be no action potential
- Stimuli might arrive from different sources. Spatial summation allows signals for multiple stimuli to be coordinated into a single response.
51
What is temportal summation?
Temporal summation is where two or more nerve impulses arrive in quick succession from the same presynaptic neurone. This makes an action potential more likely because more neurotransmitter is released into the synaptic cleft.
52
What way do synapses transmit information?
Receptors for neurotransmitters are only on the postsynaptic membranes, so synapses make sure impulses can only travel in
53
What makes up the hormone system?
The hormonal system is made up of glands and hormones
54
What are endocrine glands?
Endocrine glands are groups of cells that are specialized to secrete hormones
55
What are hormones?
Hormones are chemical messengers. Many hormones are proteins or peptides while some can be steroids.
56
How can endocrine glands be stimulated to release hormones?
- change in concentration of a specific substance
- electrical impulses
57
What are the steps of hormonal action?
- stimulus
- receptors
- hormone released
- effectors detect hormone
- response is produced
58
Why can hormones be considered highly specific?
Each hormone will only bind to a specific receptor on the membrane of a particular cell called a target cell.
Tissue that contains target cells is called target tissue.
59
Why are hormones called the first messenger?
It is called this as it carries the chemical message the first part of the way from the gland to the receptor
60
What happens when a hormone binds to its target cell?
- it activates an enzyme in the cell membrane
- the enzyme than catalyses the production of a molecule inside the cell called a signalling molecule
61
What are singalling molecules and why are they considered the second messenger in a hormonal response arc?
It carries the message the second part of the way, from the receptor to the other parts of the cell.
They activate a casacade inside the cell
62
What is the response of the hormone adrenaline?
- adrenaline is the first messenger
- it binds to specific receptors of many cells
- when it binds it triggers an enzyme in the membrane called adenylyl cyclase
- activated adenylyl cyclase catalyses the production of a second messenger called cyclic AMP from ATP
- cAMP activates a cascade
63
What are the adrenal glands and how do they work?
They are a type of endocrine gland that are found just above the kidneys.
- each gland has an outer part called the cortex and an inner part called the medulla
- the cortex and the medulla have different functions and produce different responses
64
What does the cortex do in response to stress?
The cortex releases steroid hormones like cortisol and aldosterone when you are stressed. These hormones have a role in both the short term and long term responses to stress.
65
What does the medulla do in response to stress?
The medulla secretes catecholamine hormones like adrenaline and noradrenaline when you are stressed. These act to make more energy available in the short term.
66
What are the effects of the hormones released from the cortex when stressed?
- stimulate the breakdown of proteins and fats into glucose. This increases the amount of energy available so the brain and muscles can respond to the situation.
- increases blood volume and pressure by increasing the uptake of sodium ions and water by the kidneys.
- suppressing the immune system
67
What are the effects of the hormones secreted by the medulla in response to stress?
- increasing heart rate and breathing rate
- causing cells to break down glycogen into glucose
- constricting some blood vessels so that blood is diverted to the brain and muscles
68
What are the islets of Langerhans?
They are the areas of the pancreas that contain endocrine tissue. They are found in clusters around blood capillaries. They are made up of alpha cells and beta cells
69
What do the islets of Langerhans do?
They secrete hormones directly into the blood.
70
What do alpha and beta cells in the islets of Langerhans secrete?
The alpha cells secrete glucagon
The beta cells secrete a hormone called insulin
71
What is the purpose of insulin and glucagon?
They help to control blood glucose concentration.
72
What are the characteristics of ectotherms?
- cannot control their body temperature internally
- their internal temperature depends on their external temperature
- more active at higher temperatures than lower
- have a variable metabolic rate and generate little heat themselves
73
What are the characteristics of Endotherms?
- Control their internal body temperature internally by homeostasis
- Internal temperature is less affected by external temperatures
- their activity level is independent of external temperature
- constant high metabolic rate as they generate a lot of heat from metabolic reactions
74
What are the mechanisms to reduce body temperature?
- sweating
- hairs lie flat
- vasodilation
75
What are the mechanisms to increase body temperature?
- shivering
- less sweat
- hairs stand up
- vasoconstriction
- hormones
76
How does sweating reduce body temperature?
When hot, more sweat is secreted from sweat glands. The water in the sweat evaporates from the surface and takes the heat energy away to cool the skin.
77
How does vasodilation reduce body temperature?
When hot, the arterioles near the surface of the skin dilate. This allows more blood to flow through the capillaries in the surface layer of the dermis. This means more heat is lost from the skin by radiation and the temperature is lowered.
78
How does hair lying flat reduce body temperature?
When it is hot, erector pili muscles relax so the hairs lie flat. Less air is trapped, so the skin is less insulated and heat can be lost more easily.
79
How does shivering increase body temperature?
When cold, muscles contract in spasms. This makes the body shiver and more heat is produced from increased respiration.
80
How does less sweat increase body temperature?
When cold, less sweat is produce from the sweat glands which reduces the heat loss.
81
How do erected hairs increase body temperature?
Erector pili muscles contract when its cold, which makes the hairs stand up. This traps more air and so prevents heat loss. The air creates an insulating area.
82
How does vasoconstriction increase body temperature?
When its cold, arterioles near the surface of the skin constrict so less blood flows through the capillaries in the surface layers of the dermis. This reduces heat loss.
83
How do hormones increase body temperature?
The body releases adrenaline and thyroxine. These increase metabolism and so more heat is produced.
84
What controls body temperature in mammals?
The hypothalamus
85
How does the hypothalamus control body temperature in mammals?
- it receives information from thermoreceptors
- the receptors detect internal temperature (hypothalamus/blood) or external temperature (skin/peripheral receptors)
- the receptors send impulses to the hypothalamus which then sends it to effector muscles.
86
What is the normal blood glucose concentration in mammals and what organ regulates it?
It is normally 90mg per 100cm3 of blood and it is regulated by the pancreas.
87
When does blood glucose concentration rise and fall?
It rises after eating foods containing carbohydrates
It falls after exercise as more glucose is used in respiration to release energy
88
What is the purpose of insulin?
Insulin lowers blood glucose concentration when it is too high
89
How does insulin work?
- Insulin binds to specific receptors on the cell membranes of liver cells and muscle cells.
- It increases the permeability of cell membranes to glucose, so the cells take up more glucose
- it activates enzymes that convert glucose to glycogen
- cells are able to store glycogen in their cytoplasm as an energy source.
- it also increases the rate of respiration of glucose, especially in muscle cells.
90
What is the purpose of glucagon?
Glucagon raises blood glucose concentration when it is too low
91
What is the process of forming glycogen called?
The process of forming glycogen is called glycogenesis
92
How does Glucagon work?
- glucagon binds to specific receptors on the cell membrane of liver cells
- it activates enzymes that break down the glycogen into glucose
- it also promotes the formation of glucose from glycerol and amino acids
- it decreases the rate of respiration of glucose in cells.
93
What is the process of breaking down glycogen called?
Glycogenolysis
94
What is the process of forming glucose from non-carbohydrates called?
Glucagoneogenesis
95
How is insulin secreted when high blood glucose is detected?
- when blood glucose is high more glucose enters the beta cells by facilitated diffusion
- more glucose causes the rate of respiration to increase which makes more ATP
- the rise in ATP triggers the potassium ion channels to close
- K+ ions build up in the cell
- the inside of the cell is now less negative/depolarized
- the depolarisation triggers calcium ion channels to open so they diffuse in
- this causes the vesicles with the insulin to bind to the membrane and release insulin via exocytosis
96
What is diabetes mellitus?
It is a condition where blood glucose concentration cannot be controlled properly. There are two types.
97
What is type 1 diabetes characterized at?
- autoimmune disease in which the body attacks and destroys the beta cells in the islets of Langerhans
- this means they don't produce any insulin
- so after eating blood glucose concentration remains high
- the kidney cannot reabsorb all of this glucose so some is excreted in the urine
98
Who does type 1 diabetes normally develop in?
Children or young adults. A person's risk of developing the disease is slightly increased if there is a close family history of it.
99
How could you treat type 1 diabetes?
- insulin therapy through a pump or injections
- islet cell transplantation
- monitor their diet and activity
100
What is type 2 diabetes characterised as?
- it occurs when the b cells don't produce enough insulin or the body's cells don't respond properly to it.
- This is because the insulin receptors on the cell membrane do not work
- this lead to high glucose concentration
101
Who does type 2 diabetes normally develop in?
Type 2 diabetes is normally acquired later in life and is often linked with obesity. The risk is also increased in people from certain ethic groups or with a close family history of the disease.
102
How could you treat type 2 diabetes?
- lifestyle changes like diet and exercises
- medication can be prescribed
- insulin therapy is also needed
103
What are the benefits of producing insulin using genetically modified bacteria?
- it is cheaper
- larger quantities can be produced
- make human insulin so there is less of a chance for allergic reaction
- for ethical and religious reasons some people prefer it
104
How could stem cells be potentially used to cure diabetes?
- stem cells could be grown into b cells
- the cells would then be implanted into the pancreas of a person with type 1 diabetes
- then the person is able to make insulin properly
105
How does metformin help those with type 2 diabetes?
This is usually the first medicine to be prescribed. It acts on liver cells to reduce the amount of glucose that they release into the blood. It increases the sensitivity of cells to insulin so more glucose can be taken up with the same amount of insulin
106
How does sulfonylureas help those with type 2 diabetes?
- These stimulate the pancreas to produce more insulin
107
How does thiazolidinedione help those with 2 type 2 diabetes?
- these make the body more sensitive to insulin
